1. Field of the Invention
This invention relates generally to implantable devices for interventional therapeutic treatment or vascular surgery, and more particularly concerns a vasoocclusive endoluminal coil with a helical loop forming a J-shape at one or both ends of coil, and optionally with one or more loops between each end.
2. Description of Related Art
The art and science of interventional therapy and surgery has continually progressed towards treatment of internal defects and diseases by use of ever smaller incisions or access through the vasculature or body openings in order to reduce the trauma to tissue surrounding the treatment site. One important aspect of such treatments involves the use of catheters to place therapeutic devices at a treatment site by access through the vasculature. Examples of such procedures include transluminal angioplasty, placement of stents to reinforce the walls of a blood vessel or the like and the use of vasoocclusive devices to treat defects in the vasculature. There is a constant drive by those practicing in the art to develop new and more capable systems for such applications. When coupled with developments in biological treatment capabilities, there is an expanding need for technologies that enhance the performance of interventional therapeutic devices and systems.
Vasoocclusion devices are therapeutic devices that are placed within the vasculature of the human body, typically via a catheter, either to block the flow of blood through a vessel making up that portion of the vasculature through the formation of an embolus or to form such an embolus within an aneurysm stemming from the vessel. The vasoocclusive devices can take a variety of configurations, and are generally formed of one or more elements that are larger in the deployed configuration than when they are within the delivery catheter prior to placement. One widely used vasoocclusive device is a helical wire coil having a deployed configuration which may be dimensioned to engage the walls of the vessels. One anatomically shaped vasoocclusive device that forms itself into a shape of an anatomical cavity such as an aneurysm and is made of a pre-formed strand of flexible material that can be a nickel-titanium alloy is known from U.S. Pat. No. 5,645,558, which is specifically incorporated by reference herein. That vasoocclusive device comprises one or more vasoocclusive members wound to form a generally spherical or ovoid shape in a relaxed state. The vasoocclusive members can be a helically wound coil or a co-woven braid formed of a biocompatible material, and the device is sized and shaped to fit within a vascular cavity or vesicle, such as for treatment of an aneurysm or fistula. The vasoocclusive member can be first helically wound or braided in a generally linear fashion, and is then wound around an appropriately shaped mandrel or form, and heat treated to retain the shape after removal from the heating form. Radiopacity can be provided in the vasoocclusive members by weaving in synthetic or natural fibers filled with powdered radiopaque material, such as powdered tantalum, powdered tungsten, powdered bismuth oxide or powdered barium sulfate, which can potentially be released during vascular surgery.
The delivery of such vasoocclusive devices in the treatment of aneurysms or other types of arteriovenous malformations can be accomplished by a variety of means, including via a catheter in which the device is pushed through the catheter by a pusher to deploy the device. The vasoocclusive devices, which can have a primary shape of a coil of wire that is then formed into a more complex secondary shape, can be produced in such a way that they will pass through the lumen of a catheter in a linear shape and take on a complex shape as originally formed after being deployed into the area of interest, such as an aneurysm. A variety of detachment mechanisms to release the device from a pusher have been developed and are known in the art.
One known endoluminal coil delivery system has a mechanical release mechanism for delivering a coil that has a primary coil and a bent secondary shape in the form of additional coils. The primary coil comprises a wound resilient alloy wire such as stainless steel, platinum, or shaped memory alloy formed as a straight coil, on which a bent secondary shape with coiled ends is imposed.
Other known endoluminal coils include embolic coils with offset helical and twisted shapes having multiple axially offset longitudinal or focal axes with a secondary shape with coiled ends and a middle loop. A stretch-resistant vasoocclusive coil is also known that is formed from a helically wound primary coil and a stretch resistant member, that can also have a secondary shape with coiled ends and a middle loop; and an embolization coil having a single closed loop.
Ultrasoft embolism devices are known in which the vasoocclusive or embolism forming device is made of a material that may be a braid, coil, or chain which forms a long, thin thread-like device having little rigidity or column strength, and which can be hydraulically delivered to a site within the vasculature using an injected drug or fluid flush through a catheter. The device can be made from a wide variety of materials, and may also have end-caps to prevent the device from catching on the interior of the catheter lumen or vessel.
Highly flexible coils with secondary shape are also known that form an occlusive implant that is sufficiently flexible that it can be folded upon itself and maintain that configuration. At least a portion of distal portion of the member is formed to have a first configuration in a first state and a second configuration in a second state. The distal portion second configuration has a flow resistance substantially greater than that of the proximal portion. When discharged into a region to be occluded, the proximal portion is forced into a mass around at least a portion of the distal portion secondary structure.
It has been found that single strands of small diameter nickel-titanium alloys, as well as other metal alloys, used to form vasoocclusive devices can be kinked if twisted and pulled as can occur during or after deployment from a catheter, especially if the doctor wishes to withdraw a partially deployed coil because it is somehow incorrect in size, shape or length to repair the damage to the vessel. Also, single wire coils are more likely to cause trauma to the area to be treated if the wire is of a sufficient diameter to provide adequate tensile strength. Furthermore, such small diameter wires of some of these materials such as nickel-titanium, stainless steel and the like, are not generally radiopaque with currently available equipment, necessitating the use of radiopaque markers attached to the device, with the resultant possible diminution of functionality and increased diameter.
From the foregoing, it can be seen that embolic coils have provided important improvements in occlusion devices for the treatment of aneurysms and various types of arteriovenous malformations, but that there remain important limitations in the technology presently available to fabricate these devices. It would therefore be desirable to provide a structural element that can be incorporated into a stent, guidewire, micro-coil or the like, that offers the advantages of a shape memory alloy such as a nickel-titanium alloy, and that incorporates radiopaque material in a stable configuration that is not subject to breaking during use of the device, so that the device can be visualized under fluoroscopy. The present invention meets these and other needs.